Even though the template is for MSVS it is a great place to start. It really comes down to getting gcc to create a DLL with the correct functions exported. I have done stuff like that in the past but can’t recall how to do it off the top of my head, but this type of info is easily Google-able.

MinGW should work as well if you really dont want to use the MS tools. You just need a standard DLL with the specified exports, nothing much of interest in the template project files. The template is just a guide/startpoint to copy, and the needed API files (plus ILexer.h if doing syntax highlighting) are on the main git repo.

I compile my plugins with Microsoft compiler (e.g. Windows SDK) and cygwin makefiles.
I do have MSDEV for occasional debugging.
Nothing special about NPP plugins, just compile a DLL and provide the required include paths and libraries.